No Internet Connection

If you can ping it is clearly a DNS problem. “systemctl restart network” is not correct, it’s “systemctl restart NetworkManager”. In addition, the DNS system can be restarted with “systemctl restart systemd-resolved”.

There is something not standard on the system which might cause the loss of internet: “ipv6leakintrf0” If I lookup this interface on internet I find “no access to internet after using protonvpn” . The command “nmcli c delete ipv6leakintrf0”
seems to have solved the problem. IPv6 is a problem with VPN, because they have to setup their servers and clients for both IPv4 and IPv6, otherwise IPv4 takes the VPN route and IPv6 the normal one. They try to “fix” this by blocking IPv6 name lookup.
If you have added to /etc/systemd/resolved, removed this ipv6leakintrf0 connection and restart, it should work, unless there is some residue of ProtonVPN doing stupid things. I’m still worried that there is no DHCP-originated DNS on both ethernet and WiFI. Feel free to re-enable IPv6 if there is connection again.

If you want to use VPN for some reason, you can download OVPN config files at Proton and just import them in NetworkManager. (“nm-connection-editor” if the GNOME gui does not implement it). This works perfect, but you have to activate it manually and you have to disable IPv6 manually. But there is no chance to blow up the system by some third-party fancy GUI doing things at system level.